Wastewater treatment apparatus and process therefor

ABSTRACT

Wastewater treatment plants and processes for treating wastewater are described. The wastewater treatment plant utilizes channel plug flow dynamics with attached growth media and pure oxygen or mixtures of pure oxygen and compressed air.

RELATED APPLICATION

This application claims benefit of U.S. provisional application Ser. No.61/852,031, filed Mar. 15, 2013, entitled “Wastewater TreatmentApparatus And Process Therefor,” which application is incorporatedherein in its entirety.

FIELD OF THE INVENTION

The present invention is directed to wastewater treatment plants and anew and unique apparatus and process for treating wastewater. Moreparticularly, one preferred embodiment of the invention is directed towastewater treatment utilizing channel plug flow dynamics with attachedgrowth media and pure oxygen or mixtures of pure oxygen and compressedair.

BACKGROUND OF THE INVENTION

Biological wastewater treatment in the modern era has been accomplishedby the cultivation of beneficial microorganisms being “grown” in avessel, e.g. a tank, pond, lagoon (pond with mechanical mixers), etc.,where the wastewater, such as domestic sewage, industrial wastewater,commercial wastewater, etc., can be introduced as a “food source” forthe microbes. The microbes reduce the waste, i.e. the pollutants,resulting in an acceptable treated effluent, i.e. discharge water, whichcan be discharged to streams, rivers, bays, groundwater, or reuseapplications such as landscape features, carwash water, irrigation, etc.The technology for this type of treatment has evolved exponentially inrecent years due to the advancement of scientific and engineeringunderstanding, more stringent environmental regulations, and economicadvantages in the manufacturing sector. Perhaps most important intoday's environment, there is a need to advance the usage of reclaimedwater to offset a diminishing domestic water supply.

Early in the development of biological wastewater treatment, a simplepond or lagoon was utilized as a treatment process. Wastewater wascontained after collection from, for example, a sewer network within acommunity, in the pond/lagoon where it was retained for several weeks.There, the inherent microbes would have a chance to reduce the wasteallowing “treated” water to be discharged into a water body.

Later, in an effort to accelerate the process and provide a much smallerfootprint for wastewater treatment plants (WWTPs), mechanical systemswere developed to provide the necessary air and microbe manipulation tosimulate what the sewer lagoons were doing in past years, only muchfaster and with a much smaller footprint. An advantage of these systemswas the higher level of treatment provided and, therefore, a broaderpossibility of discharge locations. These systems were termed “activatedsludge” treatment plants due to the microbes being “activated” by a highlevel of nutrients and carbon supplied by the wastewater thus allowingaccelerated growth of the organisms resulting in a very high percentageof waste material removal. “Sludge” in this context is a coalescing ofthe microbes and not the waste itself. Treatment plants of this typecould routinely remove 90-95% of the pollutants, i.e. organic matter, inthe wastewater.

In approximately the last decade, modification of the activated sludgeprocess has added another highly efficient method of removing theorganic matter from wastewater utilizing the “attached growth process”in lieu of a suspended growth process. Thus, in the conventionalactivated sludge systems, the microbes and wastewater were mixedtogether in the vessel/tank, sometimes referred to as a reactor, alongwith aeration devices such as diffusers, mixers, etc., that would keepthe water completely mixed allowing sufficient contact time for themicrobes to do their job. The development of attached growth mediasystems supplemented the suspended growth process by the addition of“media” of some sort, such as polyethylene extruded polymer, similar toa plastic honeycomb, placed into the reactor to allow the microbes toattach themselves and grow rather than being suspended in the mixedwater. This media has a high surface area to volume ratio allowing a lotof surface for the microbes to grow in a small volume of space. This hasproven to be a good system for some applications.

While known WWTPs have been useful, there is a need for WWTPs fortreating small flow, e.g. 100,000 gallons per day or less, and morepreferably 50,000 gallons per day, having a small foot print and whichis efficient in removing pollutants.

SUMMARY OF THE INVENTION

The invention is directed to a new apparatus and method using variationsof the plug flow process, the attached growth media process andsubjecting the wastewater to nearly pure oxygen (>90%) vs. air (19% O₂)or mixtures of pure oxygen and compressed air as discussed hereafter.Thus, the invention is a WWTP that uses continuous “channel” plug flowdynamics with attached growth media and pure oxygen as a source ofrequired oxygen, or a combination of pure oxygen and compressed air.

Objects of the invention include, but are not limited to, the following:(a) a reduction in the retention time within the reactor by utilizingoxygen, thus a smaller footprint and smaller basin per gallon fortreatment; (b) minimization of “washout” as with complete mix systems;(c) higher microbial populations, thus higher treatment efficiency; (d)higher reduction in recalcitrant organic compounds due to higher oxygenconcentrations in the mixed liquor; (e) reduction of short-circuiting inthe flow path as with complete mix systems; and (f) a more costeffective system in terms of space and usage. Places with smaller plotswhere space is at a premium, e.g. restaurants, carwashes, etc., willfind the invention a more viable option than the known treatmentprocesses. Additionally, offshore operations such as oil platforms andmarine vessels will find the invention very useful given available spacerestrictions and the required effluent quality.

The present invention includes an apparatus for treatment of wastewatercomprising a wastewater treatment tank for treating an influentwastewater and providing treated effluent discharge water. The tank maycomprise a tank having a bottom wall, side walls, a first end wall, asecond end wall and a cover providing access to the inside of the tank.The first end wall includes a means for receiving influent wastewaterand the second end wall includes a means for discharging effluenttreated discharge water. There are at least two baffles providing for atleast three separate compartments in the tank adapted to provide forplug flow movement of the wastewater. The compartments may includeattached growth media for treating the wastewater. There is an oxygensource or an oxygen and compressed air source connected to an airdiffuser in each of the compartments for treating the water. Theinfluent wastewater enters the tank through the first end wall and flowsthrough the at least three compartments utilizing plug flow movement andis treated by the attached growth media and the oxygen or oxygen andcompressed air to provide a treated effluent discharge water which exitsthe tank through the second end wall.

The present invention further includes a method of treating wastewatercomprising pumping wastewater into a wastewater treatment tank. Thewastewater treatment tank comprises at least two baffles providing forat least three separate compartments in the tank adapted to provide forplug flow movement of the wastewater. The compartments may includeattached growth media for treating the wastewater. There is an oxygensource or an oxygen and compressed air source connected to an airdiffuser in each of the compartments for treating the water. Theinfluent wastewater enters the tank and flows through the at least threecompartments utilizing plug flow movement and is treated by the attachedgrowth media and the oxygen or oxygen and compressed air to provide atreated effluent discharge water which exits the tank.

These primary and other objects of the invention will be apparent fromthe following description of the preferred embodiments of the inventionand from the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the specific non-limitingembodiments of the present invention can be best understood when read inconjunction with the following drawings, where like structures areindicated by like reference numbers.

Referring to the drawings:

FIG. 1 is a perspective view of the apparatus of the present invention.

FIG. 2 is an end view of the influent end of the apparatus of FIG. 1.

FIG. 3 is an end view of the effluent end of the apparatus of FIG. 1.

FIG. 4 is a top view of the apparatus of FIG. 1 showing the inside ofthe apparatus with the growth media partially cut away in the first andthird compartments and showing the wastewater flow (certain of the othercomponents of the tank are not shown for ease of reference).

FIG. 5 is taken along line 5-5 of FIG. 4 showing an elevational view ofa first baffle and an additional area for filtration or treatment of thetreated water.

FIG. 6 is taken along line 6-6 of FIG. 4 showing an elevational view ofa second baffle.

FIG. 7 is a top view of the apparatus of FIG. 1 with the growth mediaremoved and showing the diffuser components of the tank.

FIG. 8 is taken along line 8-8 of FIG. 7 and shows an elevational viewof the influent end of the tank of FIG. 1 showing the piping attached tothe diffusers.

FIG. 9 is taken along line 9-9 of FIG. 6 and is a partial elevationalview showing the outlet pipe.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the treatment of wastewater fromvarious sources. The size and scale of the present invention will varydepending upon the amount of wastewater to be treated and the nature ofthe wastewater being treated. The present invention is useful for thetreatment of wastewater from carwash facilities. The description of thepresent invention will be directed to a wastewater treatment plant fortreatment of wastewater from carwash facilities. However, it isunderstood that the invention may be directed to a number of otherwastewater treatment facilities, including as described in thisapplication.

The wastewater treatment plant of the present invention includes a tank10. The tank includes side walls 12 and 14, end walls 16 and 18, abottom 20, and a top 21. The top 21 includes a handles 21 a for openingthe top via hinges as seen in FIG. 3 and there is a center support rail21 b for the top members 21. It is understood that the top remainsclosed in operation, and there is a gasket 23 (only partially shown inFIG. 4), preferably made of foam, surrounding the upper ends of the sideand end walls to maintain the oxygen or oxygen and compressed air in thesystem. A preferred dimension for a WWTP 10 for treatment of wastewaterfrom a carwash averaging about 3,000 gallons per day is approximately 6feet in length, 3 feet in width and 4 feet in height, although thesedimensions may vary without departing from the scope of the invention.The tank may include casters 25 and may be movable.

The tank 10 receives the wastewater from a carwash and provides for thetreatment of the wastewater. The tank includes influent openings 22 inend wall 16 for receiving the wastewater and an effluent opening 24 inthe end wall 18 for discharging the treated wastewater, i.e.pollutant-reduced water. The invention uses a plug flow processproviding for a continuous path for the movement and the treatment ofthe wastewater as shown, for example, in FIG. 4. The tank is divided bybaffles 26 and 28 providing for separate compartments and a serpentinepath for the continuous flow of the wastewater, i.e. plug flow movementof the wastewater. While a presently preferred embodiment includes twobaffles 26 and 28, a different number of baffles may be used withoutdeparting from the scope of the invention.

More specifically, referring to FIGS. 5 and 6 the baffles 26 and 28 willbe described. FIG. 5 shows baffle 26 which extends vertically from thebottom 20 of tank 10 and includes an opening 40 for the water flow fromthe first compartment of the tank to the second compartment of the tank.Baffle 26 includes baffle extension members 50 and 52 which extend fromend wall 16 to the wall 70 of compartment 34 and provide reinforcementfor the tank sides. Additionally, baffle 26 includes support plates 29which provides support for the growth media 30. Such support plates 29are in each compartment as shown in FIG. 7.

Referring now to FIG. 6, baffle 28 is described. Like baffle 26, baffle28 extends from the bottom 20 of the tank vertically close to the topportion of the tank. Baffle 28 includes opening 42 for the water flow.Like baffle 26, there are baffle extensions 54 and 56 which providesupport to the side walls. It is further noted that the side walls 12and 14 also include similar extension members 58 and 60 providing meansfor attachment of plates 29 for support of growth media 30 andstructural support for tank 10. Similar to baffle 26, there are alsosupport plates 29 attached thereto and extending to the extensionmembers in the side walls of the tank.

Referring now to FIG. 7, there is shown diffuser members 36. Diffusermembers 36 are held on support plates 62. In a preferred embodiment, EDIFlexAir™ “T” Series fine bubble tube diffusers 36 are used, manufacturedby Environmental Dynamics Inc., Columbia Mo., although other branddiffusers are useful for air/O2 diffusion and mixing provided thespecifications are met. The diffuser members are connected to air supplymembers 46. Referring to FIGS. 1 and 7, the wastewater treatment plantmay utilize pure oxygen fed from an oxygen generator (not shown) toinput source 32 as the source of oxygen for the aerobic bacteria andother organisms in the oxidation of organic chemicals in various sourcesof wastewater. In the alternative, the plant may utilize pure oxygen andcompressed air, the compressed air and pure oxygen being regulated inthe specific amounts depending upon the wastewater being treated. Theoxygen and compressed air is fed to a manifold 45 and distributed bypipes 46, preferably made of PVC, to diffusers 36. Diffusers 36 providefine bubbles to accelerate the growth of the microbes for treating thewastewater.

Referring to FIG. 4, the tank includes attached growth media 30 a, 30 band 30 c for the treatment of the wastewater (media 30 a and 30 c beingshown partially cut away). As stated above, the tank includes an inputsource 32 for introducing oxygen into the system for promoting thegrowth of organisms on the growth media 30 for treating the wastewaterand removing pollutants from the wastewater. A presently preferredgrowth media is a polymer extrusion media made by Matala WaterTechnology of Taiwan. However, other manufacturers growth media may beused with the understanding that the proper surface to volume ratio andcompatibility with wastewater specifications are met. The firstapproximately ⅓ of the flow length will contain the polymer media 30 awith a minimum surface to volume ratio of about 88 ft²/ft³ followed bythe next roughly ⅓ flow length containing polymer media 30 b with aminimum surface to volume ratio of about 111 ft²/ft³. The final roughly⅓ of flow length, where polishing occurs, may have a polymer media 30 chaving a minimum surface to volume ratio of about 140 ft²/ft³. The mediadensity may be modified as needed for desired treatment results.

The hydraulic configuration of the tank is a continuous flow path, i.e.plug flow, with preferably a minimum length to width ratio through thereactor containing the media of about 8:1 depending on wastewatercharacteristics and composition. It is understood that this ratio mayfurther be in the range of about 8:1 to about 12:1. The wastewater willflow through the reactor as a fixed film process utilizing a highsurface area to volume media made from the growth media which willprovide growth sites for the aerobic bacteria and other inherentorganisms, or a bacteria “condominium” where they will grow and multiplythus reducing pollutants in the wastewater.

The tank includes an internal final compartment 34 where the reactor,i.e., aeration chambers or compartments, terminates to be used forinstallation of an additional filtration (e.g., ultra, nano, etc.) unitas needed. This compartment 34 is especially useful in meeting waterreuse requirements, although it may be optional depending on requiredwater quality. The final compartment can also be used for settling,disinfection, or chemical addition.

A preferred embodiment uses a tank constructed using 5/16 inch aluminumplate with welded joints and seams. Other materials may be utilized forthe tank construction provided that the materials are compatible withthe characteristics of the untreated wastewater and structurally capableof supporting the system components and weight of water, includingaluminum, stainless steel, fiberglass, or any extruded polymer (e.g.,plastic, high density polyethylene, etc.) The tank preferred preferablyincludes a member 37 to drain the water from all of the compartments.

The operation of the apparatus and method of the invention will now bedescribed in relation to the drawings. Referring, for example, to FIG.2, there are two inlet openings 22, e.g. a 1.75 inch diameter aluminumpipe fitting and a 1.25 inch diameter aluminum pipe fitting, forreceiving the wastewater, in this example wastewater from a carwashusing tank 10 as described above. The openings provide for receivingdifferent size pump hoses. The wastewater from a carwash is pumpedthrough one of openings 22 into tank 10, preferably in the range ofabout two gallons to about six gallons per minute. Referring to FIG. 4,the wastewater is approximately an inch above the growth media 30 andbelow baffles 26 and 28. As stated, the growth media is preferably ofdifferent densities, the least dense being in the first compartment andthe most dense being in the third compartment prior to overflow into thefiltration/chemical addition compartment 34. The water circulates fromthe first compartment through an opening 40 to the second compartmentand circulates through the second compartment through an opening 42 tothe third compartment. The circulation time may be in the range of abouteight to 24 hours depending on the oxygen concentration utilized.Thereafter, the treated water is moved from the third compartment viaoverflow pipe 44, as shown in FIGS. 8 and 9, to the final compartment 34for any additional treatment. Thereafter, the treated water is removedfrom the tank through effluent opening 24. In this example, thewastewater is treated with pure oxygen entering from an oxygen sourcethrough pipe 32 and fed to a manifold 45 which feeds conduits 46 to thefine bubble diffusers 36. This accelerates the growth of the microbesfor treated the wastewater. It is understood that the rate of the oxygenfeed may be varied thereby reducing or increasing the wastewaterdetention time in the tank. It is understood that instead of pureoxygen, a mixture of pure oxygen and compressed air may be used.

Accordingly, an objective of the present invention is a combination ofnearly pure oxygen as an oxygen source or mixed as required withcompressed ambient air with continuous plug flow hydraulics and attachedgrowth media as the substrate for bacteria to attach and grow. Thisprovides for a smaller footprint of the apparatus and process, therebyachieving lower costs, the ability to utilize the treated water insustainable applications such as water reuse, and a more completeoxidation of pollutants. An additional advantage is the reduced wastesludge volume as found in conventional suspended growth complete mixedsystems.

The invention may be used by entities requiring wastewater treatmentwith approximately less than 100,000 gallons per day of flow, andpreferably about 50,000 gallons per day, including the carwash industryfor treatment and/or reuse of wastewater from the facility, marinevessels and offshore oil platforms, remote land-based oil explorationsites, and any other commercial, industrial, and domestic applicationsrequiring wastewater treatment.

The exemplary embodiments herein disclosed are not intended to beexhaustive or to unnecessarily limit the scope of the invention. Theexemplary embodiments were chosen and described in order to explain theprinciples of the present invention so that others skilled in the artmay practice the invention. As will be apparent to one skilled in theart, various modifications can be made within the scope of the aforesaiddescription. Such modifications being within the ability of one skilledin the art form a part of the present invention and are embraced by theappended claims.

It is claimed:
 1. An enclosed wastewater treatment tank utilizing acontinuous channel plug flow process for treating an influent wastewaterand providing treated effluent discharge water comprising: a tank havinga bottom wall, side walls, a first end wall, a second end wall and acover providing access to the inside of said tank and adapted to enclosethe wastewater treatment tank to keep nearly pure oxygen or a mixture ofnearly pure oxygen and compressed air enclosed in the tank when inoperation to provide for a fully aerobic system, said fully aerobicsystem providing for a higher pollutant removal rate than a non-enclosedwastewater treatment tank that is not treated with nearly pure oxygen ora mixture of nearly pure oxygen and compressed air due to higher oxygenconcentrations in said tank; said first end wall including means forreceiving influent wastewater; said second end wall including means fordischarging said treated effluent discharge water; at least two bafflesproviding for at least three separate compartments in said tank whereinthere are vertical openings at opposite ends of said baffles and saidvertical openings are substantially the entire height of said baffles;said baffles and said vertical openings are adapted to provide forcontinuous plug flow movement of said wastewater through each of said atleast three compartments wherein said plug flow movement of saidwastewater comprises a serpentine path for continuous flow of saidwastewater through said vertical openings at opposite ends of said atleast two baffles and wherein said plug flow movement comprises a lengthto width ratio through the tank of about 8:1 to about 12:1; said atleast three separate compartments comprising at the bottom of each ofsaid compartments an air diffuser adapted to diffuse nearly pure oxygenor a mixture of nearly pure oxygen and compressed air and includingattached growth media for treating said wastewater constructed andarranged above said air diffusers and substantially filling each of saidcompartments and constructed and arranged for said wastewater to coversaid attached growth media, thereby providing for a space between saidwastewater and said cover retaining therein said nearly pure oxygen or amixture of nearly pure oxygen and compressed air; and a source of nearlypure oxygen or a source of a mixture of nearly pure oxygen andcompressed air connected to said air diffusers for treating saidwastewater, wherein influent wastewater enters said tank through saidfirst end wall and flows through the at least three compartments withsaid continuous plug flow movement and is treated by said attachedgrowth media and said nearly pure oxygen or said mixture of nearly pureoxygen and compressed air in said fully aerobic system to provide saidtreated effluent discharge water which exits said tank through saidmeans for discharging the treated effluent discharge water in saidsecond end wall.
 2. A wastewater treatment tank according to claim 1further comprising an outlet pipe in the last treatment compartmentexiting to a further treatment compartment.
 3. A wastewater treatmenttank according to claim 2 wherein said further treatment compartmentcomprises means for further treating said treated effluent dischargewater selected from the group consisting of means for additionalfiltration, means for disinfection, means for settling and means forchemical addition.
 4. A wastewater treatment tank according to claim 1wherein said tank is adapted to treat 100,000 gallons of water per dayor less.
 5. A wastewater treatment tank according to claim 1 whereinsaid tank includes means for moving said tank.
 6. A wastewater treatmenttank according to claim 1 wherein said attached growth media comprises apolymer media wherein said attached growth media in at least a firstcompartment and a second compartment of said at least three compartmentsis of a different density and the attached growth media in the firstcompartment is of a lesser density than the attached growth media in thesecond compartment.
 7. A wastewater treatment tank according to claim 1wherein said wastewater is treated with nearly pure oxygen.
 8. Awastewater treatment tank according to claim 6 wherein said attachedgrowth media in said first compartment has a surface area to volumeratio in the range of about 88 ft²/ft³ to 110 ft²/ft³; said attachedgrowth media in said second compartment has a surface area to volumeratio in the range of about 111 ft²/ft³ to 139 ft²/ft³; and saidattached growth media in a third compartment has a surface area tovolume ratio greater than 140 ft²/ft³.
 9. A method of treatingwastewater utilizing a continuous channel plug flow process comprising:pumping wastewater into an enclosed wastewater treatment tank whereinsaid tank is adapted to keep nearly pure oxygen or a mixture of nearlypure oxygen and compressed air enclosed in the tank when in operation toprovide for a fully aerobic system, said fully aerobic system providingfor a higher pollutant removal rate than a non-enclosed wastewatertreatment tank that is not treated with nearly pure oxygen or a mixtureof nearly pure oxygen and compressed air due to higher oxygenconcentrations in said tank; said wastewater treatment tank comprisingat least two baffles providing for at least three separate compartmentsin said tank wherein there are vertical openings at opposite ends ofsaid baffles and said vertical openings are substantially the entireheight of said baffles; said baffles and said vertical openings areadapted to provide for continuous plug flow movement of said wastewaterthrough each of said at least three compartments wherein said plug flowmovement of said wastewater comprises a serpentine path for continuousflow of said wastewater through said vertical openings at opposite endsof said at least two baffles and wherein said plug flow movementcomprises a length to width ratio through the tank of about 8:1 to about12:1; said at least three compartments comprising at the bottom of eachof said compartments an air diffuser adapted to diffuse nearly pureoxygen or a mixture of nearly pure oxygen and compressed air andincluding attached growth media for treating said wastewater constructedand arranged above said air diffusers and substantially filling each ofsaid compartments and constructed and arranged for said wastewater tocover said attached growth media, thereby providing for a space betweensaid wastewater and said cover retaining therein said nearly pure oxygenor a mixture of nearly pure oxygen and compressed air; a source ofnearly pure oxygen or a source of a mixture of nearly pure oxygen andcompressed air connected to said air diffusers for treating saidwastewater; and wherein influent wastewater enters said tank and flowsthrough the at least three compartments with said continuous plug flowmovement and is treated by said attached growth media and said nearlypure oxygen or said mixture of nearly pure oxygen and compressed air insaid fully aerobic system to provide treated effluent discharge waterwhich exits said tank.
 10. A method according to claim 9 wherein saidwastewater is treated with nearly pure oxygen.
 11. A method according toclaim 9 wherein said attached growth media comprises a polymer mediawherein said attached growth media in at least a first compartment and asecond compartment of said at least three compartments is of a differentdensity and the attached growth media in the first compartment is of alesser density than the attached growth media in the second compartment.12. A method according to claim 11 wherein said attached growth media insaid first compartment has a surface area to volume ratio in the rangeof about 88 ft²/ft³ to 110 ft²/ft³; said attached growth media in saidsecond compartment has a surface area to volume ratio in the range ofabout 111 ft²/ft³ to 139 ft²/ft³; and said attached growth media in athird compartment has a surface area to volume ratio greater than 140ft²/ft³.
 13. An enclosed wastewater treatment tank utilizing acontinuous channel plug flow process for treating an influent wastewaterand providing treated effluent discharge water comprising: a tank havinga bottom wall, side walls, a first end wall, a second end wall and acover providing access to the inside of said tank and adapted to enclosethe wastewater treatment tank to keep nearly pure oxygen or a mixture ofnearly pure oxygen and compressed air enclosed in the tank when inoperation to provide for a fully aerobic system, said fully aerobicsystem providing for a higher pollutant removal rate than a non-enclosedwastewater treatment tank that is not treated with nearly pure oxygen ora mixture of nearly pure oxygen and compressed air due to higher oxygenconcentrations in said tank; an influent opening in one of said wallsfor receiving influent wastewater; an effluent opening in one of saidwalls for discharging said treated effluent discharge water; at leastone baffle providing for at least two separate compartments in said tankwherein there is a vertical opening at one end of said baffle and saidvertical opening is substantially the entire height of said baffle; saidbaffle and said vertical opening are adapted to provide for continuousplug flow movement of said wastewater through said at least two separatecompartments wherein said plug flow movement of said wastewatercomprises a serpentine path for continuous flow of said wastewaterthrough said vertical opening at an end of said at least one baffleopposite from the influent opening and wherein said plug flow movementcomprises a length to width ratio through the tank of about 8:1 to about12:1; said at least two separate compartments comprising at the bottomof each of said compartments an air diffuser adapted to diffuse nearlypure oxygen or a mixture of nearly pure oxygen and compressed air andincluding attached growth media for treating said wastewater constructedand arranged above said air diffusers and substantially filling each ofsaid compartments and constructed and arranged for said wastewater tocover said attached growth media, thereby providing for a space betweensaid wastewater and said cover retaining therein said nearly pure oxygenor a mixture of nearly pure oxygen and compressed air; and a source ofnearly pure oxygen or a source of a mixture of nearly pure oxygen andcompressed air connected to said air diffusers for treating saidwastewater, wherein influent wastewater enters said tank through saidinfluent opening and flows through the at least two compartments withsaid continuous plug flow movement and is treated by said attachedgrowth media and said nearly pure oxygen or said mixture of nearly pureoxygen and compressed air in said fully aerobic system to provide saidtreated effluent discharge water which exits said tank through saideffluent opening.
 14. A wastewater treatment tank according to claim 13wherein said tank is adapted to treat 100,000 gallons of water per dayor less.
 15. A wastewater treatment tank according to claim 13 whereinsaid attached growth media comprises a polymer media wherein saidattached growth media in at least a first compartment and a secondcompartment of said at least two compartments is of a different densityand the attached growth media in the first compartment is of a lesserdensity than the attached growth media in the second compartment.
 16. Awastewater treatment tank according to claim 15 wherein said attachedgrowth media in said first compartment has a minimum surface area tovolume ratio of about 88 ft²/ft³.
 17. A wastewater treatment tankaccording to claim 13 wherein said wastewater is treated with nearlypure oxygen.
 18. A wastewater treatment tank according to claim 1wherein said attached growth media in said at least three compartmentsare of at least two different densities and the density of said attachedgrowth media of a first compartment is of a lesser density than theattached growth media of at least one of a subsequent compartment.
 19. Amethod of claim 9 wherein said attached growth media in said at leastthree compartments are of at least two different densities and thedensity of said attached growth media of a first compartment is of alesser density than the attached growth media of at least one of asubsequent compartment.
 20. A wastewater treatment tank according toclaim 13 wherein said attached growth media in said at least twocompartments are of at least two different densities and the density ofsaid attached growth media of a first compartment is of a lesser densitythan the attached growth media of at least one of a subsequentcompartment.